Intra-rater and Inter-rater Reliability of Quantitative Thigh Muscle Magnetic Resonance Imaging

Introduction: Quantitative magnetic resonance imaging (MRI) methods to quantify muscle tissue fat content are increasingly used in the evaluation of patients with inherited neuromuscular disorders. Recently, these techniques gained importance to detect disease progression and possible treatment responses. In this study, two widely used fat quantification MRI sequences (two- and three- point Dixon) were applied to assess the reproducibility and reliability of the techniques. Methods: For this clinical trial six healthy volunteers were scanned at a 3T clinical MRI scanner a total of six times on two different days (three times each) using two different fat quantification techniques: a 2-point Dixon (2-PD) and a 3-point Dixon (3-PD) technique. Each time axial sequences of both thighs were acquired. For all repeated scans and subjects a total of 660 muscles of the thighs were segmented with regions of interest (ROI) by two different raters. An interclass correlation coefficient (ICC) was used to compare inter-rater and intra-rater agreement of the different acquisition methods, regarding other potential biases such as repetition and day of the scans. Furthermore, the general accuracy of the different methods was obtained by calculating the fat fraction. Results: For quantitative MRI accessing the fat fraction in the thigh muscles, Dixon sequences have been shown to be very stable in reproducibility with ICCs of >0.9 of both inter-rater and intra-rater agreement, as well as low variability. There was no significant difference between the two sequences regarding reproducibility, although 2-PD Dixon showed a little advantage when measuring small muscles. Conclusion: In conclusion both sequences are useful for assessing fatty muscle degeneration showing a high reproducibility and reliability, with low inter- and intra-rater differences. 2-PD showed a small advantage when measuring small muscles.